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I have a 1978 Vento 350 with about 7000km on it. It has never had the get up and go I expected. I have mucked around with jets, stack length and mufflers. It has coil valve springs, an outer and inner spring for each valve. I read that that cam is probably too wild for a standard muffler and the bike would benefit from a less radical cam. How can I tell which cam is in it? I did remove the inner springs for a short while and the bike responded much better at low revs but I was concerned that it might valve bounce over say 5 to 5500 revs so I put them back in. The inlet valve is 40mm dia and it has a 32mm- Dellorto Carburetor with currently a 158 main jet up from 140 as I had to run it with a lot of choke when it was cold.
Muzz

____ Firstly,, welcome Muzz, as our latest new member !



" I have a 1978 Vento 350 "

____ Where (in the world) are you located, and where did you find your quite unique Duke-model ?



" It has never had the get up and go I expected. "

____ How did you know what to expect from it,
have you ever ridden another 350 Duke-model (by which to compare) ?



" It has coil valve springs, an outer and inner spring for each valve. "

____ I-myself unfortunately have never owned a Vento-model, so I'm unfamiliar with the valve-springs normally employed by it.
Are those paired-up dual-coil type valve-springs original-stock ? - (I'd tend to doubt so, but hopefully fellow-member Eldert can confirm exactly what the stock/original v.springs are supposed to be.)



" I read that that cam is probably too wild for a standard muffler and the bike would benefit from a less radical cam. "

____ Where exactly did you "read" that the Vento's cam is probably too wild (to be matched-up together with a muffler) ?
__ I do believe that the 350-Vento employs a uniquely extra-wild cam, and if that's really the actual case, then it MAY produce a couple extra HP only at the very highest RPM, so long as there's no (real) 'muffler' on the exhaust-system,, but with such an extra-wild cam (that's even wilder than the already TOO-wild Green & White std.350-cam), the slightly extra top-end power would come at an EXTRA-high expense of sacrificed low-end torque, (and even cause mid-range to suffer considerably [if matched along-with any kind of actual muffler] ).
So such an extremely WILD-cam would indeed make a (muffled, or not) 350-Duke pretty-much UNstreet-worthy.



" How can I tell which cam is in it? "

____ You could either try to do a degree-wheel measurement-job (so as to access it's particular valve-timing readings), or, remove the camshaft (from the cyl.head) and check it's micrometer-readings to determine the particular 'lift' of it's two separate cam-lobes.



" I did remove the inner springs for a short while and the bike responded much better at low revs but I was concerned that it might valve bounce "

____ Where did you get the idea to try that ? _ And what was the expected 'reasoning' behind actually bothering to try-out that (unusual !) test-trial ? ...
__ I assure you that removal of either the inner or outer coils (of the valve-springs) would NOT produce any even slightly notable change in power-output !! _ The only thing that could likely change, is the reliability of the valves to remain completely in concert with the cam's intended valve-timing (at the higher RPMs).
So if indeed you had in-fact actually noticed any real change in power-delivery at all, (during the lower RPM-range),, then it must've been due to something-ELSE (other than the [reduced]- strength of the valve-springs) ! _ Cuz the inner coil-springs certainly could-not be so very-strong as to make any noticeable difference in final power-output from the engine, (except possibly while at the highest RPMs, where valve-float could then likely occur).
__ You need-not take just my-own word for this claim which I'm declaring, as I'm fairly sure that most other members here could vouch for this. - (Hopefully at least, Eldert.)
(And if anyone DOES think that there's any theory at all behind how removing an inner coil-spring could possibly make any [real or noticeable] difference at all, then I am sure I'm not the only one who would like to hear of it !)


Dukaddy-DUKEs,
DCT-Bob

Hi Bob
I am in Sydney Australia and just got back from the beach. I got the bike through my friend Steve who imports bikes from Japan. (OldGold Motorcycles) I always wanted a ducati single (after rebuilding my brothers 250.) His son still has his Hailwood replica but the 250. I bought a 750SS new in 1975. It was the fibreglas tank model, 40mm carbs, no indicators etc and I kept it for 11 years. So I had some general expectations of 350s performance. It did come stock with double coil springs which were installed instead of using a Desmodromics to handle the cam. I am not an expert but after doing some calculations I decided the inner spring was unnecessary below 5500rpm so I removed it. It can however rev to 8000rpm so I eventually replaced it.
My Cals - (1978)VENTO 350 VALVE SPRINGS.
Did You Know= that at higher rpms the kinetic energy increases, so the spring deceleration increases resulting in the contact stress on the nose of the cam actually decreasing. True ??
(If the physics is true: riding at high revs is less likely to damage the cam face than riding at low revs)
Kinetic energy is:The energy possessed by a body because of its motion, equal to one half the mass of the body times the square of its speed.
• FREE HEIGHT - Ext spring 44mm - internal 35.5mm
• INSTALLED HEIGHT- ext spring length only- 35mm (valve closed )
• OPEN HEIGHT - 27mm = (8mm Lift, valve fully open)
• INSTALLED LOAD - Ext 50lbs - Inter10lb - Combined - 60lbs
• OPEN LOAD - Ext 100lbs - Inter 40lb - Combined -140lbs
• LOAD AT 20% - 76lbs (1.6mm from installed height )
• LOAD AT 80% - 124 lbs (6mm from installed height )
• VALVE WEIGHT - 76 grams
• ROCKER ARM WEIGHT - 142 grams (whole arm)
• SPRING WEIGHT - ext spring - 40 grams.
- internal - 21grams =( together 61g)
• RETAINER WEIGHT - 44 grams (with collets)
• VALVE DIAMETER - inlet - 40mm dia 82mm
• VALVE STEM DIA - 8mm
• VALVE LENGTH (TO NOTCH for COLLETS)- 82mm
• VALVE SPRING DIA (OD) –
• Ext spring OD = 33.3mm
• Internal spring OD =23.8mm a
• Rocker arm length ‘a’ 40mm
• Rocker arm length ‘b’ 80mm b
• Inner spring free length 35.5 to 36mm
Notes :
• 900 GTS have the same ext valve spring.
• Washers / retainers add 4.5 mm to valve spring installed height.
• 80lbs over 8mm = 10lbs per mm of lift

Muzz

____ Firstly, thanks for your posted-pic !
__ How about posting a picture showing the profile of the ex.cam-lobe, (as it can be seen through the [apparently currently] exposed cam-tunnel/opening) ?



" It did come stock with double coil springs which were installed instead of using a Desmodromics to handle the cam. "

____ I believe I've already heard that the newest Mototrans/Duke-singles employed coil-type v.springs, but I don't recall them being DUAL-coil setups.



" after doing some calculations I decided the inner spring was unnecessary below 5500rpm "

____ That does indeed seem quite sensible.



" Did You Know= that at higher rpms the kinetic energy increases, so the spring deceleration increases resulting in the contact stress on the nose of the cam actually decreasing. True ?? "

____ Of-course that has to be true...
The inertia of the (mass of the) valves must increase as RPMs climb, and that's why stronger v.springs must be utilized in order to keep the valves from 'floating' ... And as the valves get closer to the point of floating, they (in combination with the rocker-arms & v.springs) thus-then place next to no pressure upon the tip-ends of the cam-lobes, (after the cam-ramp has somewhat 'launched' the rocker & valve).



" riding at high revs is less likely to damage the cam face than riding at low revs) "

___ Well of-course that's somewhat fairly true but,, however just-only concerning merely the area of the cam-lobe's contact-surface which follows AFTER the lifting-ramp area of the lobe, (since the lobe's lift-ramp contact-area is still subjected to ever increasing hardship, as THAT area of the lobe's contact-surface must inject greater & greater inertial-energy into launching-open the valve, as RPM continues-on increasing).


____ Do any of all your posted facts & figures expect to provide any positive-argument for how removing the inner-springs might somehow possibly make any significant/noticeable increase/improvement in power-output at lower RPMs ? _ Cuz if so, I'm not obviously seeing it, and then need further direction (in order to possibly grasp anything of the sort).


Duke-Cheers,
DCT-Bob

Thanks for the welcome and the explanation as to why the pressure on the cam lessons at high revs. It seems quite logical now.
Regarding providing some reasoned explanation as to why the 350 seemed to rev more freely at lower revs with the inner spring removed I made the classic ‘school boy error’ by changing more than one thing at a time. Not only did I remove the spring I rejetted the carbi and changed the muffler. I have since put the original muffler back on and refitted the spring and am concentrating on the jetting.

An explanation regarding the double valve springs was offered by a Ducati mechanic friend and it went something like this:
“The single biggest fault with that engine was the valve springs. They
were completely wrong for the application. The fitted length is
incorrect and the spring strength is about 50% overdone. This wears out
cams, rockers and bevel couplings at a rate far in excess of what should
be. Leaving out the inner spring is an easy cure. Why was it included is
a good question? I suspect as a safety feature against breakage of the main spring. And how many broken springs have I ever seen? Just one in all those decades.”
However it does come back to ‘how radical is my cam?’ I need to collect a bit more info and hopefully someone can lay that question to rest.
Thanks again for your insight.
Regards
Muzz

____ Firstly,, I had sort-of hoped that there would be some further argument for the positive effect on power-output from the engine with it's valve-spring strength reduced, as I had some further info to relate on that issue.
Maybe I'll get to finding a way to insert it later.



" Not only did I remove the spring I rejetted the carbi and changed the muffler. "

____ I assume that the replacement muffler which you had tried-out, was considerably less restrictive ?



" An explanation regarding the double valve springs was offered by a Ducati mechanic friend and it went something like this:

Leaving out the inner spring is an easy cure. Why was it included is a good question?

"
____ My-own understanding as for the reasoning for the usefulness of a PAIR of coil-springs is, (other than increased-strength for greater valve-control), is that each spring happens to have a different harmonic-bounce rate at some particular RPM, so-therefore when ONE of the springs reaches a particular RPM where it will 'bounce' in harmony with the valve-gear activation-rate, the OTHER spring will not then also be caught-up within the very-same bounce-rate (at that same particular RPM).
Thus (at some harmonizing-RPM) when one of the springs becomes dumb-founded with it's very-own ringing-sensation (and THEN can't perform it's job properly), the other spring is still able to continue-on performing as it's normally expected to do (during that very particular time, at least).
So in such dual valve-spring setups,, at least one of the nonidentical coil-springs will be completely able to fully perform it's expected task, at any particular RPM-rate.



" However it does come back to ‘how radical is my cam?’ I need to collect a bit more info and hopefully someone can lay that question to rest. "

____ Have you any Ducati owner's-manual or publication which may state the valve-timing of the Vento's cam ?
I once seen such listed in some book I once had and it's stated figures for that 350-model were quite unbelievably WILD (for any engine that wasn't intended for all-out racing) !
__ Another member here once told/posted of his-own rather poor experience with the running-issues of his-own 350-Vento and it's overly wild cam... So hopefully you & he will begin conversing on such, sometime soon here.
____ I see that you've posted another picture (showing your cyl.head's exhaust valve-spring)... If that was in response to my previous request, then it seems you've misunderstood what I had actually meant to ask for. ...
I had noted in your first posted-pic that you had the camshaft bearing-support (which has "350" embossed on that camshaft-cavity cover), removed off-from the head,, thus having exposed the camshaft-tunnel/cavity, where within, can then easy be seen the (exhaust-side's) cam-lobe...
So the picture which I had wished to see would hopefully show a well lite view of that cam-lobe's profile. - (With hopes of confirming that it's indeed a 'wild' cam.)
__ As wild as I've been led to believe that the Vento-cam is, it then really isn't good for much of anything, except possibly for obtaining the MAXIMUM-power possibly available from the 350 Duke-single engine, HOWEVER, but ONLY at some extreme high-RPM (& without a 'muffler' !). _ So unless the engine is intended to be KEPT running only in that top-RPM range CONSTANTLY,, the trade-off in power-loss at lower RPMs, is very poor, and makes the 'overall power-output' average-out down-to a barely acceptable level, (at which a stock 250-Scrambler would no-doubt at least keep-up with).
So ANY other Duke-cam model would provide a beneficial increase in average/overall power-output, and most-likely make your Vento become more street-worthy, (power-wise).
__ Are you at all interested in swapping-out your Vento's camshaft ? _ Cuz perhaps someone with a std.450 would possibly be interested in swapping cams with you, (since a 450 could possibly make better use of such a wild cam).


Duke-Cheers,
-Bob

Hi Muzz (and Bob)

First off Muzz, welcome from a fellow Vento owner!

1. Cams
There were two cams available for Ventos: a 'Rapido' and a 'Lento'. Below are the timings for each (Rapido on the left, Lento on the right); and also the carb settings to go with each (Lento first, Rapido beneath). Pm me if it's not clear.



2. Performance
Quoted output of the engine was 28.8 HP with a max speed of 154km/hr or 168km/hr. Bearing in mind these were probably optimistic figures , how does yours compare? I can't pretend that mine gets near those figures ...

3. Silencer
Where did your silencer come from? IME, the larger capacity Ducati w/c singles can suffer from restrictive silencing ( I also have a 450, you see ... ). If you want, I can tell you where you can get a free-breathing stainless steel replica for the Vento, btw.

4. Carb
You may be over-fueling a tad with that size main - Mototans spec'd a 150, with a maximum of a 160. If the bike was not running off choke, I suggest it wasn't the main that was responsible, anyway. Personally, I rebuilt my carb using what Mototrans spec'd and the bike run's fine off choke.

5. What compression readings are you getting?

Un saludo

Craig

" There were two cams available for Ventos: a 'Rapido' and a 'Lento'. Below are the timings for each (Rapido on the left, Lento on the right); "

____ Thanks a lot for your helpful post Craig !
I've adjusted your posted-pic to better show just the presented valve-timing figures, (as they are both listed & depicted).
__ To anyone who has a fair grasp of camshaft valve-timing, both model-sets of the presented valve-timing figures obviously represent that of RACING-cams ! ...
The milder (but still quite wild !) figures of the "Lento" are possibly mild enough to be street-able, although likely not very street-worthy (with a city/street-sensible muffler),, while those other (even wilder) presented timing-figures stated for the "Rapido", are the same Vento valve-timing figures which I had most recalled (from some book-listing), as being more strictly for "all-out" road-racing.
(I'm not positive but, those two sets of stated timing-figures appear to me to be virtually emulating the 750-Imola & the 750SS DESMO-cams - [respectively, as the Rapido & Lento cam-versions].)
__ I'm of the opinion that the 'overall' power-performance of a 350-Vento could be much improved, (no mater whether it has the 'Rapido' or the 'Lento' cam-version),, by swapping it's camshaft for a M1/Gray-cam, or maybe even perhaps ANY other 250/350/450-OHC.Duke cam-model (other than the also too-wild G&W/F1-cam).
So if the Vento is intended to run with a street-muffler, then a camshaft swap-job is in good-order.
____ Muzz, do you know which version ('Rapido' or 'Lento') your Vento-model is supposed to be ?


Hopeful-Cheers,
DCT-Bob

Thanks Bob & Craig
It is Xmas eve here so I'll check out the cam timing as soon as I can however I may not be able to disappear into the garage xmas day no matter how much I'd like to.
Thanks for all the information. I'll go through it more slowly over the next couple of days and make some decisions on the next move.
Merry Xmas guys. Thank for all the encouragement.
Muzz

there is something odd about the timing figures .

on my degree wheel it goes from zero to 90 degrees and then back to zero again



Eldert